Heat travels along a temperature gradient, from hot to cold, at a rate that depends on the material's thermal conductivity. But when matter is scaled down to the level of individual atoms or molecules, the familiar concepts of heat diffusion by electrons and phonons that scatter from defects, impurities, or other excitations no longer apply. A one-dimensional molecule made up of a dozen atoms, say, carries heat through discrete vibrations over a length much shorter than the typical mean free path of electrons or phonons in a bulk molecular solid. And the vibrational modes can differ from those in the bulk material because of the reduced dimensionality and the lack of a periodic band structure. Accordingly, the thermal properties of a material at macro- and microscales can be very different.
The difference matters because long-chain molecules attached to tiny electrodes can be used to control the switching and transport of...
